Note that if the nodes you are showing and hiding are adjacent in the DOM and one of them is the source of the event, you could probably rewrite the whole thing to work using a single function that takes advantage of event.target and element.nextSibling.

It's easier if you set event handlers within javascript rather than inside the html code; this way it is simpler to pass variables to a single event handler. I don't understand why each of your event handlers has var data=ev.dataTransfer.getData but then doesn't do anything with the data; maybe this is something you will use later? And each of the top left and top right images is calling two separate functions when dropped (dragRightdropRight1(event),dragLeftdropRight1(event) etc), but as far as I can see the two functions do the same thing.

Anyway you can simplify as follows, with a single function drop that does something different depending on the name of the box (topLeft, topRight) and the image number (0-4).